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current split between neutral and earth

current split between neutral and earth

current split between neutral and earth

(OP)
On an overhead 4-wire multigrounded neutral distribution system, how much current is typically assumed to split between neutral and earth?

We typically assume a 50 - 50 split and use this result for voltage drop and fault calculations.  I was just wondering if this was commonly followed.

RE: current split between neutral and earth

I don't know the answer, but my guess is that it will be closer to 90% in the wire and 10% in the earth.   

RE: current split between neutral and earth

When the zero sequence impedance is calculated you have the self impedance of the neutral conductor in parallel with the fictious earth conductor. Use the two impedances separatly and calculate the current in each. Why does it matter?  

RE: current split between neutral and earth

It depends on where you are in relation to the source and load.  At the substation and the load, most current will flow in the neutral, but some current flows into the earth at each pole ground.  In the middle of the line, a larger portion will flow in the neutral.  This can be important for grounding studies and programs like SES's SPLITS can calculate how much flows in each during faults.

For voltage drop studies, you usually use the sequence impedances in a sequence phase impedance matrix rather than using a split between ground and neutral currents.

See Distribution feeder line models; Kersting, W.H. and Phillips, W.H., IEEE Transactions on Industry Applications, July-Aug. 1995, Volume: 31 , Issue: 4
 
Abstract
Starting with a modified version of Carson's equations, this paper develops distribution feeder models that can be used in the power flow and short circuit analysis of unbalanced three-phase distribution feeders. A simple line section is used to demonstrate the differences in voltage drops that occur between the various models for load conditions varying from balanced to very unbalanced  
 

RE: current split between neutral and earth

Don't know the answer but my guess on something I read decades ago, published by Puget Power, indicated that their testing indicated about 13% went into the ground and the rest down the neutral wire.  I can't rememeber the details as to what voltage or class of distribution/transmission, but it seemed to make a compelling argument for routing ground wires with the power distribution feeders on low voltage systems.  This might have been published for some regional IEEE meeting in the Pacific Northwest USA.   

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